What is XCMG XE750D Fault Code 444-5 SPN677 FMI5?

Fault Code 444-5 (SPN 677 FMI 5) indicates a low current or open circuit condition in the diesel particulate filter (DPF) differential pressure sensor circuit. This code is triggered when the engine control module (ECM) detects that the electrical current flowing through the DPF pressure sensor circuit has fallen below the manufacturer's specified threshold or that the circuit has become open.

The DPF differential pressure sensor monitors the pressure difference across the diesel particulate filter to determine soot loading levels. On the XCMG XE750D excavator, this sensor is critical for the regeneration system to function properly. When this circuit fails, the ECM cannot accurately determine when regeneration cycles are needed, potentially leading to reduced engine performance, increased fuel consumption, or complete engine derate to protect the emissions system.

Common Symptoms

• DPF warning light illuminated on the instrument cluster
• Engine derate mode activated, limiting maximum RPM and hydraulic functions
• Regeneration system fails to initiate automatic or manual cycles
• Reduced engine power during high-load operations like digging or lifting
• Stored fault codes in the ECM memory even after engine restart

Potential Causes

The most common causes for this fault code on used XCMG excavators include:

• Open or damaged wiring in the sensor harness, particularly where the harness routes near the exhaust system or frame rails (common wear point on XE750D models)
• Corroded or loose connector pins at the DPF pressure sensor or ECM connections due to moisture intrusion
• Failed DPF differential pressure sensor caused by heat exposure or internal electrical failure
• Broken sensor mounting bracket causing physical damage to sensor or wiring
• ECM internal circuit failure (less common but possible in high-hour machines)
• Rubbed-through insulation on wiring harness from contact with hydraulic lines or structural components

How to Troubleshoot and Fix Code 444-5 SPN677 FMI5

Step 1: Visual Inspection Begin by locating the DPF differential pressure sensor (typically mounted on the DPF housing). Inspect the entire wiring harness from sensor to ECM for visible damage, abrasion points, or burnt insulation. On used excavators, pay special attention to areas where harnesses pass through metal grommets or near hot exhaust components.

Step 2: Connector and Pin Inspection Disconnect the sensor connector and thoroughly inspect for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner and check for proper pin tension. Inspect the ECM connector using the same procedure.

Step 3: Electrical Testing Using a digital multimeter, perform a continuity test on the sensor circuit wiring. With the sensor disconnected, check for open circuits (infinite resistance) between the sensor connector and ECM. Verify ground continuity is less than 5 ohms. Check for short circuits to ground or power (should read infinite resistance).

Step 4: Sensor Testing Measure the sensor resistance according to XCMG specifications (typically 100-10,000 ohms depending on pressure). Replace the sensor if readings are out of specification or if the sensor shows physical damage.

Step 5: Repair and Verification Repair or replace damaged wiring harnesses, ensuring proper routing away from heat sources and moving components. Use heat-shrink tubing and dielectric grease on all connections. Clear fault codes using XCMG diagnostic software or a compatible scan tool, then perform a regeneration test cycle to verify the repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official XCMG service manual for your specific machine serial number and consult with a certified heavy equipment technician for complex electrical diagnostics or emissions system repairs.